Apparatus for wet screening



June 28, 1960 F. J. FONTEIN 2,942,730

APPARATUS FOR WET SCREENING Filed June a, 1957 2,942,730 7 APPARATUS FORWET SCREENING Freerk J. Fontein, Heerlen, Netherlands, assignor toStamicarbon N.V., Heerlen, Netherlands Filed June 3, 1957, Ser. No.663,229

Claims priority, application Netherlands June 11, 1956 7 Claims. (Cl.209- 274) This invention relates to particle separation and moreparticularly to improvements in wet screening apparatus and procedure ofthe sieve bend type, such as disclosed in U.S. patent application SerialNo. 475,251, filed December 14, 1954, of which this application is acontinuationin-part.

Such apparatus, hereinafter referred tov as a sieve bend, is disclosedin said U.S. patent application as including a screening deck,preferably curved, which may be made up either of parallel barsseparated from each other by slots, or of a plate with slot-typeopenings formed therein and extending perpendicular to the direction ofmaterial flow. In the procedure involved, the material to be separatedis fed together with a suspending liquid in layer formation tangentiallyto the concave surface of the screening deck at a pre-determined initialvelocity sothat hired States ?atent of the screening deck for directingthe material to be screened, together with a suspending liquid in layerformation, to the concave side of the screening deck at a predeterminedminimum initial velocity. The oversize or coarse fraction issuing fromthe lower end of the deck is collected in a hopper 16 and is dischargedat 18. The

undersize or fine fraction issuing through the screening deck openingsis collected in a hopper 20 and is discharged at 22. I

Referring now to Figure 2 wherein two adjacent bars of the screeningdeck 12 are shown, the numerals 1 through 6 designate successive pointsof intersection between the plane of the drawing and the correspondinglines of intersection bounding the surfaces of the bars. The numerals 7and 8 designate the theoretical lines of intersection between the topsurface 2--3 and the lateral eral surface 16. As shown,the'transiti'on'plane 1--2 the structure of the screening deck definingthe openings g when dealing with fine-grained soft materials which mustbe screened with slot openings not exceeding 0.3 mm. as, for example,starch suspensions, different problems were presented, particularly whenthe soft materials contained fibrous constituents. 7

Accordingly, it is an object of the present invention to provide animproved apparatus. and procedure of the type described particularlyadapted to separate fine-grained soft materials, especially fibrousmaterials, with a high degree of efiiciency.

Another object of the present invention is the provision of an improvedscreening deck construction operable to effectively separate mixtures offine-grained soft materials, particularly fibrous materials.

These and other objects of the present invention will become moreapparent during the course of the following detailed description andappended claims.

The invention can best be understood in conjunction with theaccompanying drawings in which an illustrative embodiment is shown.

In the drawings:

Figure 1 is a side elevational view of a screening apparatus embodyingthe principles of the present invention; and

Figure 2 is an enlarged cross-sectional view of two adjacent bars of thescreening deck of the apparatus.

Referring now more particularly to Figure 1 of the drawings, there isshown a screening apparatus of the sieve bend type, such as disclosed inthe US. patent apis flat. However, it will be understood that it may becurved, if desired.

The distance a from line 1 to plane 2--3, i.e., in the drawing, thelength of the perpendicular from point 1 to the line 23, may, accordingto the invention, not be smaller than 3 S and not larger than V2 S,,where S is the desired predetermined slot width. By preference saidmaximum distance should not exceed A S. The'requirements for thetransition plane 3--4 may be less exacting. The only requirement to bemet by this plane is that the perpendicular distance from line 4 toplane 2--3 is not greater than /2 S. By preference said maximum distanceshould not exceed S. There is, however, no objection against thisdistance being smaller than l S, or even equal to zero, in which casethe planes 2-3 and 5-4 intersect along the line 8 so that there is norear transition plane provided. If the perpendicular distance a be-- Rand R represent the radii of the circles touching the top surfaces 23 oftwo adjacent bars, said circles having their centers coincident with thecenter of the curved screen deck. According to the invention, thedifference between R and R must not exceed A part of the slot width. Thescreen decks need not have a specified radius of curvature. Such radiusmay be fixed at will, depending on the object in.view, and may even begiven a very high to infinite value, in which latter case the screendeck is flat. Even when using a flat screen deck with bars or damsaccording to the invention, finegrained fibrous materials may bescreened without any appreciable clogging, provided the material has asufliciently high flow velocity in the direction parallel to the screendeck.

Example A suspension of a fibrous material was fed at a gauge pressureof 1 atmosphere to a commercial type of sieve bend having a curvature of330, with a slot width of 0.1 mm. and a dimension a greater than A S.The under- I size, which at the start amounted to percent of the totalfeed, dropped to 60 percent after l5 minutes td Patented June 28, 1960'n i'nedi slot width, by preference not greater than /61 7 said slotwidth. The transition surface from'the top sur- From thelabove; itcan'be seen that even; with soft materials, good results may be obtainedby the present inven tion. In accordance with the principles of thepresent invention, the surface forming the transition from the flat topsufiace of each bar or dam to its lateral sur- -facefacing towards thefeed end ofthe screen must intersect the lateral surface along a linespaced from the top surface a distance which is not less than & and not.greater than half of the distance of the desired predeterface tothelateral surface facing away from the feed end a of the screen mustintersect the lateral surface along a line spaced from the top surface adistance not greater than half of the distance'of'said slot width Theradii of the circles touching the top surfaces of two adjacent bars ordams and having their centers co-incident with the center of, the curvedscreen deck must not differ by more than part of the desiredpredetermined slot width.

In addition, it is preferable that not more than perof 111 to 1.2 timesthe desired predetermined slot width;

1 ;Purthermore, not more than 10' percent of the number of slotsprovidedshould have a slot width of 0,9 10 0.8

times the desired predetermined slot width. Finally, not, more than 5tpercent. of the-number of slots provided should" have a slot widthgreater than 1.2 times the de- "sired predetermined slot width. j I

'If a screen deck. constructed ingacccrdance with {the principles of theinvention is not reversible with. respect ing awa'y'froin the feed endof the screen to meet the same exacting requirements as the side of thebars or claims facing towards the feed end' of the screen. However,itjisessential for the :line of intersection between the transitionsurface and the lateral surface to remain:

. below a given distance to the top surface, but a minimum distance'fisnot required, so that his contemplated that? no transition surface fatall will be provided on the side facing away from the Efeed'emi and thetop surfaceancl the lateralflsurfacewill simply intersect alongv astraight If the screen deckcan' b'elreversed with respectto the.

direction of flow 'of the material, as shown; both sides of -tme'bars ordams must, of course, meet the require- 'me'iits specified for thesideffacing: towards the feed end.

It'thustwill' be seen that the objects of this invention have been fullyand effectivelyaccomplished; It will be realiiedghowever', thatfth'eforegoing specific em- 'bodinient hasbeen'*shown anddescribed only forthe purposeiofillustrating the principles ofthis invention and i issubject to extensive change Vwithout departure from suchprinciples.j'lherefore, this inventionincludes' all modifications encompassedwithin the spirit and scope i of'the'following claims. I

Iclairn: p a 7 1, In an apparatus for; separating fine grained'soft' m'ate'rials suspended in a liquid acc'or'ding to size, ,a cylinq thetransition surfaces between the flat surfaces and the lateral surfacesfacing the feed end of the screening deck intersecting the lateralsurfacesalong lines spaced from' away from the feed end of the.screening deck intersecting the lateral surfaces along lines spacedfront the fiat 7 cent of. the number, ofslots provided have a slot widthsurfaces a distance not greater than onQ-halflof the distance of saidpredetermined opening width, and the radii of the circles touchingthe:flat surfaces of. two adjacent portions and having their centerscoincident with the center of curvature of said screening deck havingdistances which do notdifierby more than one-tenth of the distance ofsaid predetermined opening width.

2. A screening deck as defined in claim 1, wherein the maximumdistanceto the top surfacesof said portions of the lines. formed by theintersection of the lateral surfaces. and the transition surfaces doesnot exceed one fourth of the distance of the predetermined opening widthbetween the bars.

3. A screening deck as definedin claim 1 wherein. the distance from thelines of intersection between the transition surfaces and the fiatsurfaces to the theoretical lines of intersection between the associatedlateral surfaces and the flat surfaces is not greater than five'timesthe predetermined. opening width. a

4. A screening deck as defined in claim 1 wherein said portions are barseach. having lateral surfaces symmetrical in relation to a plane ofsymmetry and a flat surface substantially perpendicular to said plane ofsymmetry,

said lateral surfaces converging in a direction away from 1 'to'thedirectionof flow of the material'fto be screened,

it is not necessary for the side of the bars for dams fac-' layerformation tangentially at the feed end to, the con said flat surface. 11 t t 5; Arr apparatus for separating fine grained soft ma terialsaccording, to size comprisinga fixed cylindrically v curved screeningdeck having a feed end and a discharge end and a plurality oflongitudinally spaced transversely extending bars defining a pluralityofscreening openingsof' predetermined width between said feed end and saiddischarge end, and meansfor supplying ami rture of fine-grained softparticles and a suspending liquid in cave' side of the screening deck ata predetermined minimum initial velocity in a direction perpendicular tosaid bars and openings, said bars having flat surfaces. defining theconcave sideoffthe screcning deck, opposed lateral surfaces defining;thetopenings; and transition surfaces v the fiat surfaces afldistance'notgless than'one-twentieth .t'ween s'aid flat surfaces and lthelateraljsurfaeesfacing between said flat surfaces and said lateralsurfaces, the

transition surfaces; between the flat surfaces and the lateral surfacesfacing the feedendtof theg scr eeningdeck intersecting the lateralsurfaces along lines spaced from and not greater than onehalfr of'thedistance of said pre determined openingwidth, the transition surfacesbet away from the fee d'endof'thescreening deck intersecting the lateralsurfaces alonglines spaced from the" fiat surfaces 2. distance notgreater, than one-half of theidistance'ofsaid'predeterrnined openingwidth, and thev radii oflthe circlestonching the fiat surfaces of twoadjacent bars and having their centersicoincident with the center ofcurvature of said' screening deck having distanees which do' not differby more than one-tenth of the .dis-

' a t V v maximum; distancejt'o the flat surfaces of the bars of the a Vdrically curved ,screemngoeckhaving a feed end, a dis 7 I e r chargeend; and "longitudinaily spaced transverse porsaid-disehar ge end, saidportions having flat surfaces 7 V, V i 7 t 7 distance from the hnesofintersection betweenthe transidefining the material receivingside ofsaid deck, opposed lateral surfaces defining the openings, andtransition surfaces between said' flatsurfiaces and said lateralsurfaces, 7 of intersection betweenthe ta'nce offs'aid predeterminedopening width-.

6. A screening decktas defined'in claini Swherein the lines formed bythe intersection-bf the lateral 'sui'faces and the transition surfacesdoes not-exceed: one'fourth of the distancefof the predetermined openingwidth be! tween the bars. 7

7. Ascreening deck as defined in claim- 5, whereinthe and the flatsurfaces is not greater than fivetimes the predetermined opening width.

References Qited in the file of this patent UNITED STATES PATENTS 5 6FOREIGN PATENTS Great Britain Sept. 22, 1927 Great Britain June 5, 1928Great Britain June 5, 1928 Great Britain Mar. 22, 1935 Belgium Dec. 15,1952 Germany Apr. 12, 1938

